rroelke commented on code in PR #15861:
URL: https://github.com/apache/datafusion/pull/15861#discussion_r2060445809
##########
datafusion/common/src/error.rs:
##########
@@ -59,7 +59,7 @@ pub enum DataFusionError {
ParquetError(ParquetError),
/// Error when reading Avro data.
#[cfg(feature = "avro")]
- AvroError(AvroError),
+ AvroError(Box<AvroError>),
Review Comment:
I don't have the specific numbers but here's a verbose explanation of what
(the
lint)[https://rust-lang.github.io/rust-clippy/master/index.html#result_large_err]
is trying to tell us about:
```
enum MyErrorType {
Something,
SomethingElse([u8; 4096])
}
```
We can see here that the size of `MyErrorType` is 4096 (ish)
```
fn try_thing() -> Result<usize, MyErrorType> {
...
}
```
Consequently the size of `Result<T, MyErrorType>` is always at least 4096.
`Result<usize, MyErrorType>` has size 4096. To call `try_thing` we have to
allocate memory to hold that size of result. We don't return the `usize` in a
register. And most of the time we expect to see `Ok` rather than `Err` so this
makes the common case a lot worse.
Boxing the large variants fixes the issue since it reduces the size of the
variant to a pointer, which fits in a register.
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